The present invention relates to a liquid jet recording apparatus which applies energy to liquid held in a liquid channel and spouts the liquid outside through a discharge orifice, and a method for fabricating the same.
FIG. 19 is a perspective view exemplarily showing a conventional liquid jet recording apparatus, and FIG. 20 is across sectional view taken on line A in FIG. 19. In those figures, reference numeral 1 is a flow channel substrate; 2 is an element substrate; 3 is a thick layer; 4 is a liquid inlet; 5 is a common liquid chamber; 6 is a by-pass channel; 7 is a liquid flow channel; 8 is a heating resistor element; 9 is a discharge orifice; and 10 is a stepped portion. The illustrated liquid jet recording apparatus is of the thermal type. In this type of the apparatus, the energy converting element for converting electric energy to thermal energy is the heating resistor element 8. The liquid jet recording apparatus is disclosed in Japanese Patent Laid-Open Publication No. Hei 6-183002, for example. The energy converting means may be a piezoelectric element or the like.
The flow channel substrate 1 may be made of silicon, for example. Trenches to be used as a number of liquid flow channels 7 and a through-hole to be used as the common liquid chamber 5 are formed in the flow channel substrate 1 by an anisotropic etching method. One end opening of the through-hole serves as the liquid inlet 4. The common liquid chamber 5 is formed in two steps to have the stepped portion 10 by anisotropic etching process. The element substrate 2 may also be made of silicon, for example. The heating resistor element 8, which are associated with the liquid flow channel 7, are formed on the element substrate 2, and wires and drive circuits to supply electric energy to the heating resistor element 8 are further formed in the element substrate. The thick layer 3 made of polyimide, for example, is layered on those elements, wires and circuits on the element substrate. The thick layer 3 is removed of its regions for the by-pass channels 6 interconnecting the liquid flow channels 7 and the common liquid chamber 5, which are formed in the flow channel substrate 1, and the regions above the heating resistor element 8. The thick layer 3 is required for forming the by-pass channels 6, and serves as a passivating layer for protecting the wires and drive circuits formed in the surface of the element substrate 2 against liquid attack. The flow channel substrate 1 and the element substrate 2, which are thus formed, are aligned in position with each other, and bonded together.
FIG. 21 is a cross sectional view showing a liquid jet recording apparatus equipped with a manifold. In the figure, reference numeral 11 is a manifold and 12 is an adhesive. After the liquid jet recording apparatus as shown in FIG. 19 is manufactured, the manifold 11 is attached to the liquid jet recording apparatus in order to supply liquid from a liquid tank to the liquid inlet 4 of the apparatus. To attach the manifold, the adhesive 12 is applied to a portion around the liquid inlet 4 of the liquid jet recording apparatus, and the manifold 11 is bonded to the apparatus and liquid tightly sealed so as to prevent liquid from leaking outside.
In the general liquid jet recording apparatus, its purging and jetting performance depends largely on the length of the liquid flow channel if the cross sectional areas of the liquid flow channels 7 are equal to one another. Therefore, where the channel length becomes long, the flow channel resistance increases, and the amount of energy necessary for jetting the liquid becomes large or the amount of jetted liquid becomes small. This fact teaches that to design a high efficiency liquid jet recording apparatus, the length of the liquid flow channels 7 is reduced as short as possible.
If the channel length (length a in FIG. 21) of the liquid flow channel 7 is reduced, the common liquid chamber 5 is shifted to the discharge orifice 9, and the distance from the surface having an array of discharge orifices 9 to the liquid inlet 4, viz., the length b in FIG. 21, is reduced. As recalled, the portion around the liquid inlet 4 is coated with the adhesive 12, and the manifold 11 is attached and bonded to the adhesive coated portion. Therefore, if the length b between the orifice-arrayed surface and the liquid inlet 4 is short, there is a chance that the adhesive 12 applied enters into the apparatus through the liquid inlet 4. In this case, the adhesive obstructs the flow of liquid inside the apparatus, possibly causing a trouble of printing. As seen from the above facts, it is required that the channel length a of the liquid flow channel 7 is reduced as short as possible, but the length b between the orifice-arrayed surface and the liquid inlet 4 is selected to such an extent as to avoid the printing trouble. The liquid jet recording apparatus constructed as shown in FIGS. 20 and 21 uses the stepped portion 10 to satisfy the above requirements, and to improve a production yield in the manufacturing of the liquid jet recording apparatus.
The liquid for recording is supplied through the liquid inlet 4 into the liquid jet recording apparatus, and flows in the direction of an arrow in FIG. 20. The liquid flows from the liquid inlet 4 to the common liquid chamber 5, passes through the by-pass channel 6 which is formed by removing the thick layer 3, and reaches the liquid flow channel 7.
In the instance mentioned above, the flow channel substrate 1 consists of a silicon substrate. A wet anisotropic etching method using a medicine liquid, e.g., KOH solution, is known for a method for fabricating trenches serving as the liquid flow channels 7 and the through-holes as the common liquid chambers 5, as disclosed in U.S. Pat. No. 5,277,755.
FIGS. 22A to 22I are views showing a method for fabricating a liquid flow channel substrate of a conventional liquid jet recording apparatus. In the figure, reference numeral 31 designates a silicon substrate; 32 is an SiO.sub.2 film; and 33 is an SiN film.
1) FIG. 22A PA0 2) FIG. 22B PA0 3) FIG. 22C PA0 4) FIG. 22D PA0 5) FIG. 22E PA0 6) FIG. 22F PA0 7) FIG. 22G PA0 8) FIG. 22H PA0 9) FIG. 22I
A silicon substrate 31 to be used as the flow channel substrate 1 is arranged.
A SiO.sub.2 film 32 is formed on the silicon substrate 31 by thermal oxidation process.
The SiO.sub.2 film 32 is patterned to form the liquid flow channels 7 including the discharge orifices and the common liquid chamber 5 therein by a photolithography method and a dry etching method. The silicon substrate 31 used has a lattice face &lt;100&gt;.
An SiN film 33 is formed over the resultant structure by a pressure-reduction CVD method.
The SiN film 33 is patterned to form portions in which the common liquid chambers 5 are to be formed by photolithography and dry-etching process.
With a mask of the SiN film 33, the silicon substrate 31 is etched in a KOH solution. The etching process is continued till a through-hole is formed in the silicon substrate 31, and the formed through-hole is used as the liquid inlet 4.
The SiN film 33 is removed.
Using the SiO.sub.2 film 32 as an etching mask, the silicon substrate 31 is etched in a KOH solution to form trenches to be the liquid flow channels 7. In the etching process, the regions of the common liquid chambers 5 are etched to form the stepped portions 10.
Finally, the SiO.sub.2 film 32 is selectively etched away in a hydrofluoric acid solution to complete the silicon substrate 31 to be used as the flow channel substrate 1.
FIG. 23 is a plan view exemplarily showing a silicon substrate 31 to be used as the liquid flow channel substrate of the conventional liquid jet recording apparatus. Trenches serving as the liquid flow channels 7 and the through-holes to be used as the common liquid chambers 5 and the liquid inlet 4, which correspond to a number of liquid flow channel substrates, are formed in the silicon substrate 31 through the manufacturing steps as shown in FIG. 22. The silicon substrate 31 is bonded to a silicon substrate 31 including a number of element substrates 2 formed thereon, and the substrate body by the bonding of the silicon substrates is then cut into individual liquid jet recording apparatuses by dicing. A portion including an array of liquid flow channels 7 in each liquid jet recording apparatus is cut along a nozzle dicing line (indicated by a dotted line shown in FIG. 23) by dicing. The liquid flow channels 7 of the apparatus are opened in the cutting surface thereof. The openings of the liquid flow channels 7 serve as the discharge orifices 9.
As described above, the conventional method of fabricating the liquid jet recording apparatus uses the wet anisotropic etching process using the KOH solution to form the flow channel substrate 1. The wet anisotropic etching process is advantageous in that when the substrate is square when viewed in plan, the etching accuracy is high and when the substrate is etched deep as in forming the common liquid chamber 5, the etching rate is relatively high. At this time, a shape of the cross sectional area of the silicon substrate 31 is determined by the lattice face &lt;100&gt;of the substrate, usually trapezoidal or triangular. It is for this reason that the liquid flow channel 7 and the discharge orifice 9, which are formed by the wet anisotropic etching process, are triangular in cross section.
With the recent trend toward high resolution in the liquid jet recording apparatus, the pitch of the orifice array becomes smaller. In the conventional liquid jet recording apparatus, the liquid flow channels 7 and the discharge orifices 9 are uniformly triangular in cross section. Therefore, when the discharge orifice 9 is reduced in size, the cross sectional area of the liquid flow channel 7 is also reduced, so that the flow channel resistance in the liquid flow channel 7 is increased. Further, in the conventional apparatus, a part of the fluid channel like the by-pass channel is narrow and bent as shown in FIG. 20, and hence the flow channel resistance is increased.
The increase of the flow channel resistance creates the following problems. In the liquid jet recording apparatus, the resistive heater element is instantaneously heated to generate air bubbles in the liquid, and energy generated when the bubbles grow is utilized to jet liquid through the discharge orifice. Where the flow channel resistance in a portion of the channel ranging from the resistive heater element to the discharge orifice is increased, pressure generated during the growing of bubbles is inefficiently transferred to the discharge orifice. As a result, electric energy to be applied to the resistive heater element every jetting of the liquid increases. Where the flow channel resistance in another portion of the channel ranging from the common liquid chamber to the discharge orifice is increased, much time is taken till the liquid is jetted and then is re-supplied to the discharge orifice, so that a recording speed is reduced. The liquid must be sucked from the discharge orifice to stabilize the jetting operation, for example. In this case, a large pump is required for the suction. Use of the large pump leads to increase of the apparatus size.
To cope with this, the designer has attempt to use the structure where the cross sectional area of the liquid flow channel is increased but the cross sectional area of the orifice portion is decreased viz., a called constrained structure. In this connection, the thermal ink jet printer in which the channel portions located before and after the channel having the cross sectional area of 70.times.40 .mu.m are each 60.times.42 .mu.m in cross section is disclosed in the Unexamined Japanese Patent Application Publication No. Hei 7-1729. No description of a channel structure ranging from the liquid flow channel to the common liquid chamber is given in the publication, and description of the fabricating method is unclear.
The Unexamined Japanese Patent Application Publication No. Hei 7-156415 (U.S. Pat. No. 5,385,635) discloses such a printhead that the opening of the etch resistant mask is configured to increase in the middle portion of the liquid flow channel when the anisotropic etching process is applied. Also in this printhead, a part of the liquid flow channel is narrowed and bent as the by-pass channel, and as a result, the flow channel resistance increases.
Another printhead is disclosed in the Unexamined Japanese Patent Application Publication No. Hei 4-296564 (U.S. Pat. No. 5,132,707). In the printhead, the liquid flow channel is entirely formed with a thick film material, and the nozzle portion is constricted when viewed in plane. Actually, it is technically difficult to accurately fabricate the entire liquid flow channel with the thick film material.
The Examined Japanese Patent Application Publication No. Hei 6-84075 discloses another printhead designed such that a recess deep to such an extent as not to shut off the liquid flow channel is formed in the ceiling near a thermal energy acting portion, and the recess is used to supplementarily supplying recording liquid. The approach by merely recessing the ceiling near the thermal energy acting portion fails to solve the problem of the flow channel resistance increase.